Osmotic therapeutic systems manufactured in the form of osmotic devices for the precision administration of drugs with control of delivery patterns and with extended operational delivery times are known in U.S. Pat. Nos. 3,845,770 and 3,916,899. The systems disclosed in these patents are made of a single layer wall that surrounds a reservoir containing a drug. The wall is permeable to the passage of an external fluid, impermeable to the passage of drug, and it has a portal for delivering drug from the system. The systems disclosed in these patents are extraordinarily effective for delivering a drug that is soluble in the fluid and exhibits an osmotic pressure gradient across the wall against the fluid, and also for delivering a drug that has limited solubility in the fluid and is mixed with an osmotically effective compound that is soluble in the fluid and exhibits an osmotic pressure gradient across the wall against the fluid. The systems release drug by fluid being imbibed through the wall into the reservoir at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall producing a solution of soluble drug, or a solution of soluble compound containing drug which solution in either operation is dispensed at a controlled rate over a prolonged period of time. While the above systems represent an outstanding and pioneer advancement in the osmotic art, and while they are useful for dispensing innumerable drugs to the environment of use, it has now been found these osmotic systems can have a unique laminated wall that unexpectedly improves the usefulness and the integrity of the systems.
That is, the systems of this invention comprise a unique laminated wall having a thin lamina formed of a material possessing a given set of properties in laminar arrangement with a supporting, preferably thicker lamina possessing a different set of properties. The system embracing a laminated structure made according to the present invention can have properties such as permeability to external fluids, impermeability to drugs and solutes, and physical and chemical integrity be selected independently, and also have the mode and manner of drug release be made programmable based on the laminae comprising the structured, laminated wall. For example, the wall can comprise a laminae consisting of a thin to very thin lamina facing the environment and a thicker supporting lamina facing the reservoir with each possessing different properties. The lamina facing the environment can be made of a semipermeable material permeable to fluid, impermeable to drug, inert in the presence of drug, and by being thin to very thin in the semipermeable lamina allows an increase in the delivery rate. The lamina facing the reservoir can be made of a microporous material selected to exhibit low to zero resistance to the passage of fluid and drug compared to the semipermeable lamina, which microporous lamina provides structural support for the semipermeable lamina and does not interact with drug and fluid. The structure of the laminated wall allows the use of more inert, polymeric lamina materials which are usually less permeable. The invention's use of a thin rate controlling semipermeable lamina assures that a sufficiently high rate can be maintained for the system. The therapeutic systems made available by this invention and embodying the unique laminated wall thereby functions according to a pre-selected built-in optimal program of drug presentation.